Production Of Citric Acid From Corn Meal By Aspergillus Niger

Production of citric acid from corn flour by Aspergillus niger was investigated and optimized in this study.Based on the correlation analysis of parameters, the basal technology for citric acid fermentation was determined:the critical concentration of dissolved oxygen at 40%, fermentation temperature at 37.5℃, initial pH between 3.8-4.1. The by-product organic acids produced in citric acid fermentation were investigated by HPLC method. The results showed that they were oxalic acid, cis-aconitic acid and anti-aconitic acid, but their concentration were all very low. The citric acid fermentation process was optimized then. Seed culture age reduced from 28 h to 22 h. With this optimized seed culture age, total fermentation time was shortened by 7 h, and the production of citric acid increased too. Halving the liquefying time reduced the initial concentration of dissolved phosphorus in medium, which is benefitial to both of growth control and early citric acid production. Supply CO2 during fermentation seemed to be an effective method for elevated citric acid production (14.2%) and conversion efficiency increased from 87.3%to 94.6%, too.The effects of liquefying conditions on medium components were investigated. The most efficient conditions were:95℃, water to corn meal ratio 3.17:1, and 160 rpm. The influence of enzyme dosage, pH of medium, liquefying time on component of the liquefied corn meal was investigated too. It was proved to be benefitial to citric acid fermentation with a large enzyme loading, natural pH without control, and short liquefying time conditions.